Recently, various types of portable electronic devices, such as a notebook computer, a Personal Digital Assistant (PDA) and a mobile phone, all need a miniature power generation unit. Since the weight and use convenience of a conventional rechargeable cell are greatly limited, various replaceable power generation units are developed, in which the development of a fuel cell manufactured with a micro-electromechanical technology is the most rapid, and the fuel cell has advantages such as fast reaction rate, high heat dissipation efficiency and space saving.
The fuel cell enables hydrogen atoms in fuel to be dissociated with an electrochemical reaction, and simultaneously release electrons to generate current. Substances as hydrogen gas, methanol, natural gas or gasoline may be directly used as the fuel. FIG. 1 is a schematic structural view of a conventional Direct Methanol Fuel Cell (DMFC) 10. Diluted methanol is input into a passage of an anode 11, diffuses and penetrates a Gas Diffusion Layer (GDL) 121 of a porous structure, and when the methanol contacts a catalyst 131, the following chemical reaction is generated.Oxidation reaction: CH3OH+H2O→CO2+6H++6e−
Electrons generated by the oxidation reaction are collected by the GDL 121, and supply power needed by a load 80 through an external line, and then the electrons are transferred to a GDL 122 at an end where a cathode 15 is located. Also, after the reaction, the product of carbon dioxide still exists, so the anode 11 still needs to emit the carbon dioxide to the atmosphere. A porous thin film 14 is located between the GDL 121 and the GDL 122, which separates the anode 11 from the cathode 15, and allows protons (H+) to penetrate and reach the catalyst 132 to perform a reduction reaction, and the reduction reaction formula is as follows.
      Reduction    ⁢                              ⁢                            ⁢          reaction      :                                    3            2                    ⁢                      O            2                          +                  6          ⁢                                          ⁢                      H            +                          +                  6          ⁢                                          ⁢                      e            -                                ->      3    ⁢                  ⁢          H      2        ⁢    O  
Oxygen needed in the reduction reaction is supplied to the GDL 122 through the passage in the cathode 15, and meanwhile waste water generated by the reduction also needs to be drained to the outside. The total reaction of the oxidation reaction and the reduction reaction is as follows.
      Total    ⁢                              ⁢                            ⁢          reaction      :                                    CH            3                    ⁢          OH                +                              3            2                    ⁢                      O            2                                ->            CO      2        +          2      ⁢                          ⁢              H        2            ⁢      O      
However, the reduction reaction of the DMFC 10 at the cathode 15 generates water, while if the water is not treated in time, the water is accumulated in a reaction region of the cathode 15, so it is difficult for the oxygen needed by the reaction of the cathode 15 to enter, and thus the reduction reaction cannot be generated, thereby causing decrease of the cell power. Currently, many research teams are discussing to actively introduce reactant gas at the cathode, and use forced air flow to dry the water generated at the cathode, thereby solving the problem of the water accumulation, or remove the water in a capillary force manner.
Metz T et al. also propose a technology of removing water generated at a cathode in the capillary force manner in a document (Metz T, Paust N, Müller C, Zengerle R, and Koltay P “Passive water removal in fuel cells by capillary droplet actuation” Sensors & Actuators: A. Physical. 143 p. 49-57), in which one drainage passage is placed on a GDL of the cathode, the front end of the passage is designed to be tapered inward, and the distal end is one rectangular passage; the foregoing tapered design can suck the water from the outside to inside of the passage, then store the water in the rectangular passage, and finally transfer the water to two sides of the passage in a corner flow manner to allow a water absorption material to absorb. However, in the document, the technology of guiding oxygen into a reaction zone of the cathode is not disclosed, while since waste water cannot be quickly drained, the guiding the oxygen to enter may seriously affect the power generation performance.
Additionally, S. C. Yao et al. mention a manner of utilizing gravity in a document (Alyousef Y and Yao S C “Development of a silicon-based wettability controlled membrane for microscale direct methanol fuel cells” Microfluid Nanofluid 2 p. 337-344), in which water generated at a cathode flows downward under the effect of gravity, and then a micro-pump is utilized to enable the water to return to an anode to participate in a reaction. A porous array structure is adopted, and hydrophilic/hydrophobic treatment is performed periodically at a sidewall of a pore of this structure, so that gas/fluid can be selectively allowed to enter and leave pores treated with different surface treatment. After the fluid is generated from the reaction zone, the fluid can flow into a hydrophilic pore array and then leave the reaction zone, while a hydrophobic pore array always maintains dry to provide a path for oxygen diffusion. However, in the document, the drainage speed is not increased with the corner flow technology, the water can form fluid drops only through the hydrophilic pore array and then be concentrated in the gravity manner, and finally the micro-pump delivers the collected water back to the anode.
To sum up, in order to improve the fuel cell power, a cell electrode capable of quickly separating and delivering gas/fluid is needed, and therefore, the present invention particularly proposes an electrode structure capable of guiding a product to leave and guiding reactant gas to enter, and a passive fuel cell having the electrode structure.